President Obama tore into those in Congress and the media who deny climate change, calling them a radical fringe that threatens the future by shutting down debate even among those who might agree with the warnings.

"Today's Congress is full of folks who stubbornly and automatically reject the scientific evidence. They'll tell you climate change is a hoax, or a fad. One says the world might actually be cooling," he said Saturday in a commencement address to 8,000 graduates of UC Irvine.

"Many others duck the question by saying, 'Hey, I'm not a scientist.' Let me translate. What that means is, 'I accept that man-made climate change is real, but if I admit it, I'll be run out of town by a radical fringe that thinks climate science is a liberal plot.'"

Obama stressed the stakes for graduates and their generation, urging them to join the political fight.

"I tell you all this not to discourage you," he said in an outdoor ceremony at Angel Stadium. "I tell you this to light a fire under you. As the generation getting shortchanged by this inaction, do not for a second accept that this is the way it has to be."

To underscore his argument, he stressed that a majority of scientists and the public believe the threat is real.

"The climate change deniers suggest there's still a debate over the science. There's not," he said. "The talking heads on cable news suggest public opinion is hopelessly deadlocked. It's not."

Stymied by Congress, Obama has been using executive actions where he can to curb emissions that contribute to climate change. His administration recently announced proposed regulations to curb power plant carbon emissions that create greenhouse gases, a major contributor to climate change.

On Saturday, he also announced a new $1 billion initiative that would challenge local communities to develop innovative ways to rebuild or plan infrastructure to better respond to the effects of climate change, such as flooding and storms.

The $1 billion National Disaster Resilience Competition would be financed from existing appropriations, but would require communities declared as disaster zones in recent years to compete for the cash by proposing new ways to rebuild or plan.